In the processing of semiconductor devices, such as transistors, diodes, and integrated circuits, a plurality of such devices are typically fabricated simultaneously on a thin slice of semiconductor material, termed a substrate, wafer, or workpiece. In one example of a semiconductor processing step during manufacture of such semiconductor devices, the substrate or other workpiece is typically transported into a reaction chamber in which a thin film, or layer, of a material is deposited on an exposed surface of the substrate. Once the desired thickness of the layer of material has been deposited, the substrate may be further processed within the reaction chamber or transported out of the reaction chamber for further processing.
The substrate is typically transferred into the reaction chamber by way of a wafer handling mechanism. The wafer handling mechanism lifts the substrate from a position outside the reaction chamber and inserts the substrate into the reaction chamber through a valve or door formed in a wall of the reaction chamber. Once the substrate is transferred into the reaction chamber, the substrate is dropped onto a susceptor. After the substrate is received on the susceptor, the wafer handling mechanism is withdrawn from the reaction chamber and the valve is closed such that processing of the substrate can begin. In an embodiment, a susceptor ring is located adjacent to, and surrounds, the susceptor upon which the substrate is disposed during processing. Such rings can serve to minimize heat loss from the edge of the wafer/susceptor during processing and/or house components such as temperature sensors.
FIGS. 1-3 illustrates a known reaction chamber 10 and substrate support assembly 12 typically used in the Epsilon® tools produced by ASM America, Inc. of Phoenix, Ariz. The substrate support assembly 12 is configured to receive and support a substrate 18 within the reaction chamber 10 when the substrate 18 is being processed. The substrate support assembly 12 includes a susceptor support member 14 and a susceptor 16. A susceptor ring assembly 20 surrounds the susceptor 16 within the reaction chamber 10. The susceptor ring assembly 20 provides a small gap between the inwardly-directed edge of the susceptor ring and the outwardly-directed edge of the susceptor. The susceptor ring assembly 20 can absorb radiant energy to reduce or eliminate heat loss from the outer edge of the susceptor 16 and substrate 18 during processing. The susceptor ring assembly 20 typically used in the Epsilon® tool includes a susceptor ring, which includes a lower susceptor ring 22 and an upper susceptor ring 24, and a susceptor ring support member 26.
During processing of a substrate within a reaction chamber, the temperature within the reaction chamber varies and may have a temperature range between room temperature and about 1200° C. When the temperature within the reaction chamber is raised and/or lowered, the various components within the reaction chamber thermally expand or contract accordingly. The commonly known substrate support assembly 12 and susceptor ring assembly 20 illustrated in FIGS. 1-3 are located within the reaction chamber 10 and thermally expand and/or contract as the temperature within the reaction chamber 10 is raised or lowered. The susceptor support member 14 and the susceptor ring support member 26 are typically formed of an insulating material, e.g., quartz, and the susceptor 16, lower susceptor ring 22, and upper susceptor ring 24 are formed of a heat-absorbing material, e.g., SiC-coated graphite. The susceptor ring support member 26 includes a plurality of pins 28 that are received by the susceptor ring to positively locate the susceptor ring within the reaction chamber 10.
The lower susceptor ring 22, as shown in the bottom plan view of FIG. 3, includes a first aperture 30, a second aperture 32, and a third aperture 34 formed therein. The apertures are configured to receive a pin 28 (see FIG. 1) extending from the susceptor ring support member 26. The first aperture 30 is located adjacent to the leading edge 36 of the upper support ring 24, closest to the gas inlets, and the second and third apertures 32, 34 are located adjacent to the trailing edge 38 of the upper support ring 24, closest to the gas exhaust. The first aperture 30 is formed as a circular hole through a projection extending from the lower susceptor ring 22. The first aperture 30 is sized to provide a snug fit between the hole and one of the pins 28 extending from the susceptor ring support member 26. The second aperture 32 is formed as a circular hole that is larger than the outer diameter of the pin 28 received therein. The third aperture 34 is formed as an elongated slot configured to receive another of the pins 28 therein.
As the temperature increases in the reaction chamber 10 during processing of a substrate 18, the lower and upper susceptor rings 22, 24 thermally expand. The susceptor 16, lower susceptor ring 22, and upper susceptor ring 24 are typically formed of graphite, and the susceptor support member 14, susceptor ring support member 26, and pins 28 are typically formed of quartz. The components (16, 22, and 24) formed of graphite have a significantly larger coefficient of thermal expansion relative to the coefficient of thermal expansion of the components (14, 26, and 28) formed of quartz, wherein the graphite components expand more than the quartz parts in response to the same temperature change. In order to accommodate these differences in thermal expansion, the second and third apertures 32, 34 are larger than the corresponding pins 28 received therein, the lower and upper susceptor rings 22, 24 are able to freely thermally expand such that as the susceptor ring expands or contracts, the pins 28 translate within the second and third apertures 32, 34. However, because the first aperture 30 provides a snug fit with a corresponding pin 28, the susceptor ring is prevented from thermally expanding away from the susceptor near the leading edge 36 of the upper susceptor ring 24. The leading portion of the susceptor ring is substantially pinned relative to the susceptor as the trailing portion of the susceptor ring is free to thermally expand. The lack of movement of the susceptor ring due to thermal expansion near the leading edge of the susceptor ring typically reduces the gap between the susceptor ring and the susceptor near the leading edge while the gap between the susceptor ring and the susceptor near the trailing edge increases.
As a result, the restrained movement of the leading portion of the susceptor ring relative to the susceptor creates uneven gap spacing between the susceptor ring and the susceptor. The uneven gap spacing between the susceptor ring and the susceptor at the various locations about the susceptor may cause temperature non-uniformities on the susceptor and the substrate being processed. Further, if the susceptor ring is not properly aligned relative to the susceptor, the gap between the susceptor ring and the susceptor may be reduced to the point where the susceptor ring contacts the susceptor. Because the susceptor typically rotates about its vertical axis during processing, any contact between the susceptor and the ring can create particles that can become deposited on the surface of the wafer or other problems with the processing of the substrate.
A need therefore exists for a self-centering susceptor ring that is capable of thermally expanding evenly about a susceptor such that the gap between the susceptor ring and the susceptor expands or contracts substantially evenly about the susceptor.